a) Field of the Invention
The invention relates to a display device using an optical member such as liquid crystal, and more particularly to a display device having a drive circuit therein.
b) Description of the Related Art
A liquid crystal display devices (LCD) formed by adhering a pair of plates having predetermined electrode wiring mutually with a small gap therebetween and charging a liquid crystal into the gap to form a capacitor having the liquid crystal as a dielectric layer to form pixels, or an organic electroluminescence (EL) display device using organic EL capable of controlling an amount of emission by a quantity of electric current are used extensively as displays in the fields of OA equipment and AV equipment in view of advantages of being compact, thin, and low in power consumption. Especially, an active matrix LCD, which is formed with a thin film transistor (TFT) connected as a switching element to each pixel capacitor in order to control writing and retention of a display signal voltage, can display high resolution images are now standard.
FIG. 11 is a plan view showing the entire LCD, in which reference numeral 1 is a TFT substrate positioned at the back of the drawing, 2 is a counter substrate positioned toward this side of the drawing, and 3 is an edge sealing material for adhering the substrate 1 with the substrate 2 and made of a thermosetting adhesive agent such as an epoxy resin or a resin which is cured by irradiation of UV light. A small gap is formed between the TFT substrate 1 and the counter substrate 2 by a spacer (not shown), and the sealing material 3 is partly cut away to form an injection hole 31. The liquid crystal is injected into the gap through the injection hole 31, and the injection hole 31 is tightly sealed with a sealing material 32.
The TFT substrate 1 has TFT formed using polycrystalline silicon (p-Si) as a channel layer on the substrate. The substrate 1 has thereon a display area 4, which has a plurality of gate lines GL and drain lines DL arranged to intersect to one another and pixel electrodes PX formed at the intersections and connected to pixel TFTs SE to form one of pixel capacitors, a gate driver 5 formed around the display area 4 to supply a scanning signal to the pixel TFTs SE, a drain driver 6 which mainly comprises a bidirectional shift register and an analog switch and supplies a display signal voltage to the pixel TFTs SE in synchronization with scanning of the gate driver 5, and a control circuit 7 which changes the shifting direction of the shift register to switch the operation directions of the drivers 5, 6. These drivers 5, 6 are formed of p-Si TFTs having the same configuration as the display area 4. Since the p-Si TFT has a sufficient operation speed, it can configure not only the pixel TFTs SE but also the peripheral drivers for driving them. Thus, a driver built-in LCD having such drivers incorporated into the display panel can be provided. Such TFTs are covered with a flattening insulating film of acrylic resin, SOG (spin on glass), BPSG (Boro-Phospho Silicate Glass) or the like. The pixel electrodes PX are formed on the flattening insulating film in the display area 4, and connected to the pixel TFTs SE through contact holes formed in the flattening insulating film. Reference numeral 8 denotes signal-input terminals of such drivers.
The counter substrate 2 has a common electrode 9, which forms the other of the pixel capacitors, formed entirely to correspond with the display area 4. Although FIG. 11 shows circuitry on the front side of the substrate 2, the circuitry may be formed on the back side to oppose the TFT substrate 1. The pixel capacitors are formed to comprise the liquid crystal and the common electrode 9 divided by the pixel electrodes. The common electrode 9 is partly extended to a corner of the substrate 2 to form a second counter electrode (common electrode) connection terminal 91. The TFT substrate 1 has a counter electrode signal input terminal 81 for the common electrode 9. The counter electrode signal input terminal 81 is routed to a first counter electrode connection terminal 83 formed on an area corresponding (oppose) to the counter electrode connection terminal 91 by a route line 82. And, the first and second counter electrode connection terminals 83, 91 are mutually adhered with a conductive adhesive agent 92.
FIG. 12 is a partly enlarged plan view of an LCD. Gate driver 5 comprises a vertical shift register 51 and a buffer portion 52 which are formed along the vertical side in the drawing. Drain driver 6 comprises a horizontal shift register 61 formed along the horizontal side in the drawing and a sampling portion 62 consisting of analog switches corresponding to respective columns. The analog switches are controlled to turn on/off by the respective output phases of the horizontal shift register 61 to sample a display signal voltage from the original image signal which is externally supplied in synchronization with a dot cycle allocated to each column in each horizontal cycle and output to each column.
The epoxy resin or UV resin used for the sealing material 3 may contain water content which survives after drying when applied, atmosphere water content, impurity ions, or the like, and the flattening insulating film as the base of the sealing material 3 may be polarized. Thus, TFTs below the flattening insulating film cause a back channel effect, and an operation threshold voltage varies. Therefore, in the configuration that the sealing material 3 is formed to cover the areas of the gate driver 5 and the drain driver 6 as shown in FIG. 11, a logical circuit such as the shift register is located just below the sealing material 3. When the operation characteristics of the respective TFT elements are changed, malfunction may occur, possibly resulting in equipment failure.
Further, even if the characteristics of the TFT elements are only slightly changed, when the curved portion of the outer edge line of the sealing material 3 is formed to locate on the drain driver 6 as shown in FIG. 12, the respective output phases of the drain driver 6 differ in operation between those in the area just below the sealing material 3 and those in the area not below the sealing material 3. As a result, the display characteristics are different between the columns of the display area 4 corresponding to the output phases below the sealing material 3 and those in the area other than the sealing material 3 on the side of the gate driver 5, the display characteristics also differ between the rows with the corresponding phases of the gate driver 5 just below the sealing material 3 and those in the area not below the sealing material 3. In the drawing, the shaded (with lines rising toward the right side) area in the display area 4 has the corresponding shift register 51 or 61 of the gate driver 5 or the drain driver 6 in the area just below the sealing material 3, and the area not shaded has the corresponding shift registers 51, 61 in the area other than the sealing material 3. The area not shaded is free from being changed the display characteristics, while the hatched area has the display characteristics varied. Thus, the shaded area is seen different from the other area. A large stress is applied to the outside edge of the curved portion of the sealing material 3 to affect on the characteristics of the TFT elements positioned below it. Therefore, the area having the phases of the corresponding drivers 5, 6 on the curved portion of the sealing material 3 is seen different from the other area. Thus, the mixed presence of the areas with different display characteristics in the display area 4 results in degrading the display quality.
If the control circuit 7 is defective in operation, the operating directions of the drivers 5, 6 cannot be changed, and general versatility of the LCD having drivers therein is degraded.
In the invention, an adhesive agent is applied so that its edge lines extend linearly in a direction of the longitudinal sides of the drive circuit area.
Accordingly, the phases in the drive circuit are prevented from being influenced differently by the adhesive agent, and the mixed presence of areas having different displays in the display area can be prevented.
The adhesive agent may preferably be formed to detour around the control circuit area so that the operation directions of the drive circuit are switched suitably.
The adhesive agent may also be preferably formed to detour around the drive circuit area and/or the control circuit area so that the drive circuit and the control circuit are prevented from being made defective due to influence of the adhesive agent.
It may also be preferable that the drive circuit comprises a drive signal output portion based on the output from at least the shift register and each output phase of the shift register, and the adhesive agent is formed to detour around the shift register area and/or the control circuit area.
Accordingly, the shift register and the control circuit are prevented from being defective in operation due to an influence of the adhesive agent.
The adhesive agent may further preferably be formed to fully cover the shift register area or the drive signal output portion.
In this way, an influence applied by the adhesive agent is equal to all the phases in the shift register, and the operation characteristics of all the phases are uniform. Therefore, the mixed presence of areas having different displays in the display area can be prevented.
The adhesive agent may also preferably fully cover the drive circuit area. Influences applied to all the phases in the drive circuit by the adhesive agent are then equal, and the operation characteristics of all the phases are uniform. Therefore, the mixed presence of areas with different displays in the display area can be prevented.
As described above, in the display device with the drive circuit built in according to the invention, the drive circuit is prevented from being made defective by the adhesive agent used to adhere a pair of opposed electrode substrates, and high quality displays can be produced.